The present invention relates to the technical field of adsorptive materials based on activated carbon which have some reactive/catalytic activity as well as adsorptive properties.
More particularly, the present invention relates to a process for producing an activated carbon having reactive/catalytic activity additization by endowing/impregnating the activated carbon with at least one metal-organic framework substance (MOF material).
The present invention further relates to an activated carbon having reactive/catalytic activity additization, obtainable by the process of the present invention, and also to a corresponding activated carbon as such.
The present invention further relates to uses of the activated carbon having catalytic/reactive activity/additization in the manufacture of filters and filter materials of any kind and also in the manufacture of protective materials of any kind. The present invention further relates to uses of the activated carbon according to the invention as a sorption store, as a catalyst/catalyst carrier and also for chemical catalysis and as gas sensor or in fuel cells. The present invention further relates to the uses of the activated carbon of the present invention for sorptive applications and/or for gas cleaning and also for gas purification and/or for the removal of noxiants. The present invention finally relates to the use of the activated carbon according to the invention for reprocessing/providing cleanroom atmospheres.
The present invention further relates to protective materials as such, obtained by using the activated carbon according to the invention and/or including the activated carbon according to the invention. The present invention further relates to filters/filter materials as such, obtained by using the activated carbon according to the invention and/or including the activated carbon of the present invention.
Chemical and biological noxiants/poisons and thus toxic substances based on organic and inorganic compounds/chemistries may occur in various forms in the built and/or natural environment and are an immense potential hazard to human life and health. The underlying chemical and biological noxiants/poisons may differ widely in origin:
For example, harmful or even toxic compounds are often by-produced in industrial processes as undesired secondary/waste products which, if improperly handled and, more particularly, if freely released into the environment, are a source of high danger and/or high toxic potential.
Chemical/biological noxiants/poisons are also employed as chemical/biological warfare agents, interchangeably also known as chemical warfare agents (CWAs). Warfare agents of this type continue to be part of the arsenal of many countries. In addition, owing to their in-principle ease of production and simplicity of transportation, warfare agents of this type represent a constant risk that they will also come into the possession of terrorist groups, so there is a permanent danger of misuse for that reason as well. The best-known warfare agents are, in particular, mustard gas, also known by the synonym of “HD”, soman, sarin, phosgene and also tabun.
There are numerous prior art methods reportedly offering a basis for ensuring some protection against the above-adduced noxiants/poisons, in particular against toxic substances of industrial origin and also warfare agents. These include, for example, the employment of liquid/gas-impervious barrier materials processable in an appropriate manner, for example into protective suits. However, the materials employed for this are sometimes deficient in wearing comfort, since they prevent not only air but also water vapor transfer.
Adsorption materials, particularly in the form of activated carbon, are a further possibility for ensuring some protective function against chemical/biological noxiants/poisons. The adsorption material, in particular the activated carbon, may in this context be employed in the form of filters, for example on the basis of filters for NBC protective masks or the like. Employing adsorption materials of this type in protective suits is a further possibility, in which case the adsorption materials employed for this purpose are often fixed on a supporting structure. This makes it possible in principle to also realize air and water vapor pervious materials, which serves in particular to increase the wearing comfort of the protective suits manufactured on this basis—and this without significantly reducing the protective function.
Activated carbon has highly non-specific adsorptive properties—which ensures a protective function with regard to numerous chemical/biological noxiants/poisons of various types/characteristics—and a high adsorption capacity and so is the most widely used adsorbent in this context. Statutory requirements as well as increasing environmental awareness are leading to an increasing demand for activated carbon.
Activated carbon is generally obtained by carbonization (also known as pyrolysis) and subsequent activation of carbonaceous starting compounds, the preference being for starting compounds which lead to economically viable yields. This is because the weight losses caused by detachment of volatile constituents during carbonization and by the subsequent burn-out during activation are appreciable. For further details regarding the production of activated carbon in general, reference may be made for example to H. v. Kienle and E. Bäder, “Aktivkohle and ihre industrielle Anwendung”, Enke Verlag Stuttgart, 1980.
The constitution of the activated carbon produced—whether finely or coarsely porous, firm or brittle, etc.—is also dependent on the starting material. Customary starting materials are coconut shells, charcoal and wood (e.g., waste wood), peat, bituminous coal, pitches, but also particular plastics, which play a certain part in the production of activated carbon cloths inter alia.
Various forms of activated carbon are used: carbon powder, splint coal and/or granulocarbon, molded carbon and also, since the end of the 1970s, activated carbon in spherical form (“spherocarbon”). Spherical activated carbon has a number of advantages over other forms of activated carbon, such as carbon powder, splint coal, granulocarbon, molded carbon and the like, making it valuable or even indispensable for certain applications: it is free-flowing, abrasion resistant, i.e. dustless, and hard. Spherocarbon, for example, is very much in demand for particular uses because of its specific shape, but also because of its high abrasion resistance.
Spherocarbon is currently still mostly produced in multi-step processes which are very costly and inconvenient. The best-known process consists in spherules being produced from coal tar pitch and suitable asphaltic residues from the petrochemical industry and oxidized (to render them unmeltable), and then carbonized and activated. For instance, spherocarbon is also obtainable in a multi-step process proceeding from bitumen. These multi-step processes are very cost-intensive, and the associated high price of the spherocarbon thus obtainable is a bar to many uses where spherocarbon actually ought to be preferred on account of its properties.
WO 98/07655 A1 describes a process for producing activated carbon spherules wherein a mixture comprising a distillation residue from diisocyanate production, a carbonaceous processing aid and optionally one or more further added substances is first processed into flowable spherules and subsequently the spherules thus obtained are carbonized and then activated.
The prior art further discloses the production of spherocarbon by carbonization and subsequent activation of virgin or spent ion exchangers containing sulfonic acid groups, or by carbonization of ion exchanger precursors in the presence of sulfuric acid with subsequent activation, wherein the sulfonic acid groups and the sulfuric acid, respectively, have the function of a crosslinker. Processes of this type are described for example in DE 43 28 219 A1, DE 43 04 026 A1 and also DE 196 00 237 A1 including the DE 196 25 069 A1 application for a German patent of addition.
The prior art further discloses processes wherein the production of activated carbon, in particular spherocarbon, is effected by carbonization and subsequent activation of sulfonated divinylbenzene-crosslinked polystyrenes (i.e., sulfonated styrene-divinylbenzene copolymers), cf. for example DE 10 2007 050 971 A1.
There are specific uses, however, where it is not just the geometry and/or outer shape of the activated carbon which is of decisive importance, but also its porosity, in particular the total pore volume and the adsorption capacity on the one hand and the distribution of the pores, i.e., the fraction of micro-, meso- and macropores in relation to the total pore volume, on the other. Especially the porosity can be intentionally varied through the choice of starting materials and also through the processing conditions. In the context of the present invention, the term “micropores” refers to pores having pore diameters of less than 2 nm, whereas the term “mesopores” refers to pores having pore diameters in the range from 2 nm (i.e., 2 nm inclusive) to 50 nm and the term “macropores” refers to pores having pore diameters of more than 50 nm (i.e. >50 nm).
Its good adsorptive properties help activated carbon into employment for a multiplicity of uses. For instance, activated carbon is employed for example in medicine or pharmacy, but also in the food industry. Activated carbon is also widely used for filter applications (e.g., filtration of gases and liquids, removal of unwanted or harmful/toxic gases, etc.).
Activated carbon is employable in particular in adsorption filter materials, including in particular specifically in protective materials against poisons, such as chemical-biological warfare agents, for example NBC protective apparel.
Air and water vapor pervious protective suits against chemical warfare agents are known for this purpose in particular; these air and water vapor pervious protective suits often have an adsorption filter layer comprising activated carbon to adsorb the chemical poisons.
There are disadvantages entailed by the use of porous adsorbents in the form of activated carbon in that, in particular, the capacity for adsorbing the chemical/biological noxiants/poisons in question is limited. This is because a specifically durable attachment of the adsorbed substances in the porous system of the activated carbon employed leads to a certain degree of saturation/exhaustion, limiting the uptake/adsorption of further noxiants. There is also a risk that the adsorbed noxiants/poisons will desorb again from the noxiant/poison-laden adsorbents and so will be released again.
On the other hand, activated carbon as such does not always have the ideal adsorption spectrum/bandwidth for the particular application, in particular with regard to the adsorption of inorganic chemistries/compounds, such as ammonia, hydrogen sulfide and hydrogen cyanide, or the like. Gas treatment and/or purification in particular requires adsorption materials having optimum adsorption capacities for inorganics as well as organics.
The prior art in this context discloses an additization of activated carbon on the basis of so-called salt impregnations, in particular in the form of metal salts present as such in the activated carbon. More particularly, permeable adsorptive filtering systems, in particular permeable adsorptive filtering systems based on activated carbon, are often additized with a catalyst to enhance the adsorptive performance/spectrum, in that this is reported to not only provide a certain degree of regenerability to the activated carbon but also to broaden the adsorption spectrum with regard to inorganic substances in particular.
An example of a specific impregnation employed in this context is a so-called ABEK impregnation, which has a catalytic effect with regard to specific toxic substances. In this context, type A relates to certain organic gases and vapors having a boiling point>65° C., for example cyclohexane. Type B relates to certain inorganic gases and vapors, for example hydrogen cyanide. Type E relates to a degrading/protecting effect with regard to sulfur dioxide and other acidic gases and vapors. Type K finally relates to a protective function with regard to ammonia and organic derivatives of ammonia. For further information, see the relevant European standard EN 14387 (January 2004).
The disadvantage with conventional impregnations of activated carbon is the fact that some of the adsorption capacity of the activated carbon, in particular with regard to organic compounds, is lost by the impregnation, which thus also reduces the adsorption and hence neutralization of chemical noxiants. The performance capability of the activated carbon is thus at times adversely affected by the impregnation processes known from the prior art.
In addition, a conventional additization of activated carbon with a catalytic/reactive component does not always attain the desired efficacy. Particularly the problem of noxiants/poisons, in particular warfare agents, striking through at high concentrations is also not always solved by this principle; on the other hand, the desired efficiency is often not achieved at very low concentrations of to-be-removed noxiants or unwelcome gases (in the reprocessing of air for cleanroom conditions, for example), since effective adsorption only ensues at higher concentrations. Moreover, any conventional additization of activated carbon, in particular with metal salts, requires relatively large amounts of impregnant and, on the other hand, the desired homogeneous loading/additization of the adsorbents with the impregnating material is often not achieved in a satisfactory manner.
Against this background, approaches have been pursued in the prior art to provide adsorption materials having not only some reactive/catalytic activity but also improved adsorption properties with regard to inorganic toxic substances in particular.
EP 1 738 823 A2 in this context relates to a catalytically active unit comprising a supporting material, wherein the catalytically active unit or the supporting material comprises polymeric particles, wherein the polymeric particles include at least one catalytically active component, wherein organic-inorganic hybrid polymers in this regard, containing metals and/or heteroatoms in addition to silicon alkoxides and/or Si—O—Si units. The materials described, however, primarily act not as adsorbents but as catalytically active particles as such.
DE 10 2005 022 844 A1 describes a process for separating odorants from gases wherein a gas is said to be brought into contact with a filter which contains a porous metal-organic framework material, wherein the framework material includes at least one at least two-pronged organic compound bound coordinatively to a metal ion. Yet there are disadvantages in the occasionally costly and inconvenient production process and also the limited adsorption performance of the resulting adsorption material.
WO 2009/056184 A1 relates to a sorption filter material including an adsorbent based on a metal-organic framework substance and also, as a further adsorbent, a spatially separate sorbent based on activated carbon. The particles of the metal-organic framework substance on the one hand and also the particles based on activated carbon, on the other, may be fixed on a supporting material. The resulting sorption filter material, however, is not ideal with regard to its physical properties in particular, since particularly the particles based on the metal-organic framework material may have a lower stability and/or attritional hardness. In addition, the adsorption properties resulting from the separate arrangement of activated carbon on one side and of metal-organic framework substance on the other are not always ideal particularly under extremely high noxiant exposure in that adsorption properties across the area of the sorption filter material are sometimes not unitary with regard to organic and/or inorganic compounds.